Particle acceleration method and apparatus



March 31, 1959 PARTICLE ACCELERATION METHOD AND APPARATUS Filed Jan. 2. 195B D. B. LANGMUIR H'AL 3 Sheets-Sheet 1 1 FROM aom nzssao R s nca o. c,. VOLTAQE gouach Soumzr.

DAV/D B. LANGMuIQ WA RREN A. MARRISO/V INVENTORS.

ATTORNEYS.

March 31, 1959 D. B. LANGMUIR EI'AL I 2,880,337

PARTICLE ACCELERATION METHOD AND APPARATUS Filed Jan. 2. 1958 3 Sheets-Sheet 2 DAV/o B LA/voMw/z H WARREN A. MA RRASON l'' 'I'M' INVENTORS.

Hg, 5 BY Rodn- ATTORNEYS.

United States Patent '2,sso,ss1

PARTICLE ACCELERATION METHOD AND APPARATUS David B. Langmuir, Santa Monica, and Warren A. Marrison, Palos Verdes Estates, Calif assiguors, by mesne assignments, to Thompson Ramo Wooldrldge lne., Cleveland, Ohio, a corporation of Ohio Application January 2, 1958, Serial No. 706,671

19 Claims. (Cl. 313-63) This invention relates to a method and apparatus for accelerating particles to a relatively high velocity, that is, to a velocity appreciably in excess of thermal velocities and, while not limited thereto, is herein described with reference to an arrangement for elcctrostatically accelerating extremely fine particles such as dust-like particles or large molecules.

According to the invention microscopic particles, such as dust particles, large molecular ions, or extremely fine metallic powder, are given an electrical charge and are then electrically accelerated. A work piece, for example a tungsten carbide tool blank, is subjected to the resultant stream of high velocity particles for desirably shaping the work piece, the shaping being produced by the sandblasting-like impact of the particles on the work piece.

According to another embodiment the stream of charged particles is produced by a space charge limited electrostatic gun. The stream of particles is realized by first charging the particles so that a mass to charge ratio of from about 1,000 to 1 to about 10,000 to l is produced (the ratio being that of the atomic mass to elementary charge), and then subjecting the charged particles to an electrostatic potential of at least about 10,000 volts and a particle velocity of up to about 50 kilometers per second. The stream of charged particles forms a thrust-producing arrangement useful in providing propulsive power for a space vehicle.

In the drawing, wherein like reference characters refer to like parts:

Figure l is an illustration of a work piece shaping arrangement according to the invention;

Figure 2 is an enlarged fragmentary view of a portion of the apparatus of Figure 1;

Figure 3 is schematic illustration of a modification of a portion of the apparatus of Figure 1;

Figure 4 is a partially schematic illustration of a thrust producing arrangement according to another embodiment of the invention; and

Figures 5 to 8 are graphs illustrating various particle acceleration parameters.

Figure 1 illustrates apparatus for shaping a work piece, such as a tungsten carbide tool blank 10, by subjecting the work piece to a stream of high velocity particles 12. The particles 12 used in the apparatus of Figure l are extremely fine particles having radii of the order of from .01 to 1 micron. The particles 12 may, for example, be of iron. One type of iron found useful in practicing the invention is that known in the art as carbonyl iron powder. This iron powder is produced by the known process in which iron is first heated in an atmosphere of carbon monoxide gas where gaseous iron pentacarbonyl, Fe(CO) is formed; and then further heated whereupon the gas deposits metallic iron as submicroscopic crystals which form microscopic spheres.

The work piece shaping referred to is realized by means of the sputtering or erosion eflects of the particles on the work piece. The shaping apparatus, disposed within an evacuated chamber provided by a bell jar 14, is made up of mechanical acceleration means 15, particle charging means 17, and electrostatic acceleration means 19. The mechanical acceleration means 15 ineludes a container 16 mounted for vibratory motion on a vibrator 18 and is used to separate the minute particles from each other by imparting kinetic energy to them; the charging means 17, which may be an electron gun of the type common in electron tubes, is used to establish an electric charge on each of the separated particles as they emerge from the container 16; and the electrostatic acceleration means 19, which may be a conventional configuration of electrodes of the type common in ion and electron accelerators and which is used to accelerate the charged particles to the desired velocity.

The apparatus of the invention will now be described in greater detail in connection with Figures 1 and 2. The particles 12 to be accelerated are disposed within a particle storage bin in the form of a rigid container 26. The particle storage or source container 26 has a central region 24 defined by a flexible membrane 28 (which may be a material such as rubber) disposed within the container. A conventional worm or screw type conveyor 30 is disposed along a central portion of the container 26 for feeding the particles out of the central region 24 referred to at a predetermined, regular rate. The conveyor 30 includes a feed screw 32 housed within a grill-like sleeve 34 having apertures 36 through which the particles 12 are forced by pressure applied by the flexible membrane 28. The region 22 of the particle source-container 26 between the flexible membrane 28 auttfthfirigidlwslis of the container is subjected to compressed gasgiiuc hlas compressed air from an inlet 37 leading to"a'-compr essetl air source (not shown), for moving partieies"withinthe storage region 24 inwardly to the feed-screwial The feed screw 32 is driven by a conventional motorand gear reduction unit 38. As the feed screw 32rotates, pai'ticles are moved through the apertured portion of the sleeve 34 and out of thestorage region 24 and into the container 16 of the mechanical acceleration means 15.

The function of the mechanical acceleration means 15 is to provide the electrostatic acceleration means 19 or ion gun with a copious stream of particles. This stream of particles emerges from the container 16, through a nozzle 39, with a velocity that is relatively low compared to the final ejection velocity of particles from the ion gun. For example, the particlesmay emerge from the first container 16 at a velocity of less than about one percent of the final ejection velocity from the ion gun. The container 16 of the mechanical acceleration means 15, which is preferably of a non-magnetic material such as, for example, brass if the particles 12 are of a magnetic material such as the iron referred to, is coupled to the rigid particle source container 26, as by means of a flexible coupling 41, and is mounted on a conventional vibrator mechanism 18. The vibrator mechanism 18 may be of any of the conventional oscillatory vibrator mechanisms known in the art and is preferably, for example, one capable of vibrating the container 16 with an acceleration (in directions A) of the order of times the force of gravity over a distance of about one-eighth inch. Particles entering the container 16 are thus given sufiicient kinetic energy to elfect a random distribution of the particles within this container. Since the only exit from this container 16 is through an orifice 40 (in the nozzle 39) adjacent to the electrostatic acceleration means 19, particles 12 drift out of this container 16 by virtue of the kinetic energy imparted to them by the vibrator 18. As the particles emerge from the container 16 they are subjected to bombardment by electrons 42 from the electron gun 17 for placing elecassess? tric charges uponthe particles. In the particle charging arrangement illustrated in Figure 1 a beam of electrons 42, from a cathode 46, is accelerated by an anode 44 and is caused to pass through the region through which the particles pass. The electrons 42 are accelerated to a velocity such that collisions between the electrons 42 and the particles 12 cause the particles to absorb electrons and thus be charged negatively; The negatively charged particles are then subjected to acceleration by an apertured first acceleration electrode 48 biased by a steady or pulsed high voltage direct current power supply (not shown). After passing through the aperture in the first electrode 48 the particles are subjected to a succession of further accelerations by a series of suitably positioned and shaped apertured acceleration electrodes 49, 51, 53, 55, 57, and 59. Each of the particles 12 is thus accelerated to a relatively high velocity (for example to a velocity of the order of 5 kilometers per second for a one micron radius particle subjected to a 100,000 volt acceleration potential or a velocity of 50 kilometers per second for a .01 micron radius particle subjected to the same voltage) and travels at this high velocity to its target, the work piece 10.

Since the resultant high-energy beam of particles 12 exhibits strong sputtering or erosion effects, it is desirable to focus the particles through the accelerating electrode 48 and to avoid impingement of the particles on any portion of the electrostatic accelerating system 19 lest erosion of electrodes be effected. One of the accelerating arrangements that is preferred in practicing the invention uses an initial accelerating arrangement exemplified in an accelerating gun of the type well-known in the art as the Pierce gun. Such a gun type is described, for example, in Theory and Design of Electron Beams, chapter X, J. R. Pierce, published by the Van Nostrand Company, New York city, N.Y., 1949.

While in the charging means 17 of the apparatus of Figure l the particles to be accelerated are first negatively charged and then subjected to a positive electrostatic acceleration field, the particles may instead be positively charged and then subjected to a negative acceleration field. Also, while the charging means 17 of the apparatus of Figure l is exemplified as an electron gun, it will be appreciated that other particle charging means may instead be used. For example, if the particles are to be given a positive charge, the particle charging may instead be effected by subjecting the particles to be accelerated to a beam of positive ions, or to X-ray radiation as illustrated in Figure 3.

In the particle charging apparatus indicated schematically in Figure 3 an X-ray tube 56 is connected to an appropriate power supply 58 and is positioned to irradiate particles 12 emerging from the nozzle orifice 40. The X-ray radiation, on bombarding the particles 12, gives rise to the release of photoelectrons from the particles. The particles thus become positively charged. The charged particles are then accelerated by a series of negatively charged accelerating electrodes 48, 49, 51, 53, 55, 57, and 59.

As shown in Figure 4, the electrostatic particle propulsion arrangement according to the invention may also be used to provide thrust for use in such applications as space vehicle propulsion. According to the invention relatively massive ions or particles, having a mass of from about L000 to about 10,000 nucleons (that is, neutrons and protons) per elementary charge, are subjected to electrostatic acceleration. Applied voltages of the order of at least about 10,000 volts (and preferably of the order of about 100,000 volts) may thus be used without an exhaust velocity greater than about 50 kilometers per second; consequently, the efiiciency of low exhaust or particle emission velocities (i.e., less than about 50 kilometers per second) is realized with the eficiency of high voltages (voltages of the order of at least 10.000 volts). Exhaust velocities greater than of the order of about 50 kilometers per second are generallyundesirable since, as is known, the required propulsion energy (the energy required per unit amount of thrust in a propulsion system) increases in proportion to the exhaust velocity.

Referring now to Figure 4, the electrostatic propulsion arrangement of the invention is in general similar to the particle acceleration apparatus described with respect to Figures 1 and 2. The portions of the apparatus of Figure 4 corresponding to those of Figures 1 and 2 are designated with the same numerals as those in Figures 1 and 2, primes being used in referring to the apparatus of Figure 4. The propulsion arrangement to be described is adapted to be operated in a vacuum such as exists in space beyond the earth's atmosphere. As in the case of the apparatus of Figures 1 and 2, particles 12' from a particle storage region 24' are subjected successively to mechanical acceleration means 15', particle charging means 17, and electrostatic acceleration means 19'. However, in the apparatus of Figure 4 the particles 12' are charged positively instead of negatively as described with respect to Figures 1 and 2. To this end the particles 12' are subjected to a stream of positive ions from a positive ion source 47'. Positive ion sources are well known in the art; the ion source 47' may, for example, be of the type described in U. S. Patent 1,809,115, granted to R. H. Goddard. The flexible membrane 28' assures the feed of particles to and along the feed screw 32' in the absence of gravity, the compressed gas source for the region 22' between the membrane and container walls taking the form of a tank 20' of compressed air.

While the particles emitted from the propulsion apparatus of Figure 4 may be charged either positively or negatively and then subjected to an electrostatic acceleration field of a sign opposite that of the sign of the charged particle, it is preferable to charge the particles positively as by subjecting the particles to bombardment by a stream of protons or positive ions. The acceleration of positively charged particles is preferred since a higher charge level can be produced on a particle when it is charged positively than when it is charged negatively. The reason for this is that the fundamental upper limit on the charge on a particle is set by the value of the electric field (at the surface of the particle) that would cause charges to tend to leave the particle. In the presence of electric field intensities greater than about 4x10 volts per centimeter electrons would be emitted if the particles were negatively charged. Surface inhomogeneities on a non-spherical particle, sharp points in particular, would enhance electron emission so that this upper limit might not be realized in practice. 0n the other hand, if the particle is charged positively, a higher charge level can be reached since field emission of positive ions from particles having substantially smooth surfaces (such, for example, as carbonyl iron particles aforementioned) is negligible at electric field intensities lower than about 2x10 volts per centimeter. Thus, it appears that attainable electric charge densities areabout five times higher for positively charged particles than for negatively charged ones. Furthermore, surface inhomogeneities are apparently less troublesome in the case of positively charged particles since a sharp point on the surface of a positively charged particle would be dulled by positive ion emission.

Electrical neutrality of the space vehicle should be maintained when thrust is produced by the exhaust of a stream of charged particles 12. To this end half of the particles emitted from the vehicle should be positively charged and the other half negatively charged. Thus, if the stream of particles providing acceleration are positive ions 12', an electron gun 52' may be provided to dis charge particles 54' having a charge opposite that of the thrust producing particles 12'. If the neutralizing particles54' have amuchhighereharge tornus ratio than the particles in the main beam, such as is the case when the neutralizing particles are electrons, the effect of the neutralizing particles upon the mass and power requirements'of the space vehicle are negligible.

For optimum performance the beam of particles 12' should be substantially completely space charge limited, that is, the particle acceleration field at the particle emitter, the nozzle 39', should be substantially zero so that there will be no force exerted upon the emitter nozzle. The reason for this is that in the absence of space charge the lines of force which start at the accelcrating electrode 48 would end on the emitter noule 39' so that no resultant thrust would be provided. The eflfect of the space charge is to electrostatically shield the emitter nozzle 39 so that the lines of force end upon the moving charged particles. Thus, in the space charge limited gun there is then a net thrust upon the accelerating electrode system 19', balanced by the momentum imparted to the space charge. To the extent that the particle flow is not space charge limited, lines of force will extend from the first accelerating electrode 48' to the emitter nozzle 39' (or other fixed portions of the apparatus) and the thrust imparted to the apparatus will be correspondingly reduced.

It will now be shown that for any values of space vehicle velocity increment (velocity added to the vehicle), space vehicle acceleration time, and power supply specific power (ratio of electric energy produced per unit power supply mass), there is an optimum particle or space vehicle exhaust velocity that gives a minimum ratio of total initial space vehicle mass to payload mass. It will be seen that space vehicles may be realized with the payload constituting a substantial fraction of the total initial space vehicle weight.

Consider a space vehicle with characteristic parameters as follows:

The structural mass is not considered separately in this analysis, and is assumed prorated among the three masses M Mp, and M defined above. For purposes of this analysis it is also assumed that the efiiciency of conversion of electric power to kinetic energy in the exhaust stream is 100 percent.

We can now write the following equations:

M,,=aw (1 where 1/ a is the specific power (that is, the ratio of electrical energy produced per unit power supply mass) of the electrical power supply,

Combining these Equations 2 and 3,

a 1 P/ L PI L ML therefore and s is! ME. E E ML cum (6) so that M1' am-2k l+m q( (7) If y and C are expressed in kilometers per second, and a in kilograms per kilowatt, Equation 7 becomes This Equation 8 is plotted in Figures 5, 6, and 7 to illustrate the variation of initial to payload mass ratio connection with launching rockets from the ground, but

rather in propelling space vehicles, for example in propelling a vehicle already placed in a satellite orbit which had to be moved farther from the earth over a period of many days. It is to be noted that:

(l) The initial vehicle mass to payload mass ratio, M /M ratio, increases rapidly as specific power, a, increases, becoming infinite at a finite value of a;

(2) With constant specific power, a, the M /M ratio becomes infinite at values of particle exhaust velocity C above and below the optimum value of exhaust velocity;

(3) The sharpness of the minimum increases markedly when the minimum value of M M becomes larger than about 2; and

(4) For a given value of specific power, a, great improvements in initial to payload mass ratio can be realized by increasing t the duration of time allowed for acceleration to the desired increment of velocity v Equation 8 can also be written A IOOOEF 9 2(MI YL This Equation 9 expresses performance in terms of the dimensionless parameters M /M C/v and r /v using units of seconds, kilograms per kilowatt, and kilometers per second.

Equation 8 is plotted in Figure 8 in a form illustrating that there is an optimum particle or exhaust velocity, C, that gives a minimum time of acceleration, t for any given initial to payload mass ratio, M /M By differentiating and equating to zero one obtains the following Equation 10 which defines the optimum value of particle exhaust velocity, C:

This Equation 11 is solved graphically in Figures 5 to 7 for optimum values of (CIv as a function of X.

This solution is represented by the curves 6., 61, and 62 in, respectively-Figures 5, 6, and 7, these curves being minima in Figures 5, 6, and 7. Thus it is seen that there is an optimum particle or exhaust velocity for a minimum initial to payloadmass ratio, other parame ters remaining constant. Also, since propulsion performance is dependent upon the relation between acceleration time and specific power, ineonveniently high values of specific power can be avoided by allowing more time for acceleration. Furthermore, a high ratio of total mass to payload mass appears to be easily realizable for a space vehicle in a satellite orbit; for example, it appears that a ratio of over 50 percent may be easily realized for a 10 kilometer per second velocity increment over a time interval of 10" seconds for a spe, cific power of about 10.

From the foregoing it is seen that the electrostatic particle acceleration arrangement according to the invention not only provides a means for desirably shaping work pieces, but is also advantageous in other fields, such as in providing an eficient propulsion means for space vehicles.

What is claimed is:

1. Apparatus of the kind described; comprising: mechanical particle acceleration means having a particle exit therein; particle charging means adjacent to said exit and adapted to impart to particles emerging from said exit a charge of a predetermined sign; and electrostatic particle acceleration means positioned to accelerate particles subjected to said charging means and adapted to be connected to a voltage source of a sign opposite said predetermined sign.

2. Particle acceleration apparatus, comprising: particle source means; conveyor means connected to said source means for the transport of particles therefrom; mechanical particle acceleration means connected for receipt of particles from said conveyor means and adapted to impart kinetic energy to said particles; and electrostatic particle acceleration means adjacent to said mechanical acceleration means and positioned to subject particles from said mechanical acceleration means to an electrostatic acceleration field for further increasing the kinetic energy of said particles.

3. Particle acceleration apparatus, comprising: mechanical particle acceleration means, said means having an orifice therein for the release of particles therefrom; and electrostatic particle acceleration means adjacent to said orifice and positioned to subject particles from said mechanical particle acceleration means to an electrostatic acceleration field for imparting additional kinetic energy to said particles.

4. The apparatus claimed in claim 3 wherein said electrostatic particle acceleration means is a space charge limited particle acceleration gun.

5. Particle acceleration apparatus, comprising: particle source means; conveyor means connected to said source means for the transport of particles therefrom; mechanical particle acceleration means connected for receipt of particles from said conveyor means and adapted to impart kinetic energy to said particles; particle charging means adjacent to said mechanical acceleration means and positioned to impart an electrical charge to particles subjected to said acceleration means; and electrostatic particle acceleration means adjacent to said mechanical acceleration means and positioned to subject charged particles from said mechanical acceleration means to an electrostatic acceleration field for further increasing the kinetic energy of said particles.

6. Apparatus of the kind described, comprising: mechanical particle acceleration means having a particle exit therein; X-ray apparatus adjacent to said exit and adapted to impart a positive charge to particles emerging from said exit; electrostatic particle acceleration means positioned to accelerate particles subjected to said charging means and adapted to be connected to a negative voltage source.

7. Apparatus of the kind described, comprising: me-

chanical particle acceleration means having a particle exit therein; a positive ion source disposed adjacent to said exit and adapted to impart a positive charge to particles emerging irons said exit; electrostatic particle acceleration means positioned to accelerate particles subjected to said charging means and adapted to be connected to a negative voltage source.

8. Particle acceleration apparatus, comprising: mechanical particle acceleration means, said means having an orifice therein for the release of particles therefrom; and space charge limited electrostatic particle acceleration means adjacent to said orifice and positioned to subject particles from said mechanical acceleration means to an electrostatic acceleration field for imparting additional kinetic energy to said particles.

9. Apparatus of the kind described, comprising: particle source means adapted to store particles at least as small as about one micron in radius; mechanical particle acceleration means connected to receive said particles from said source means and having a particle exit therein; a particle charging-gun disposed adjacent to said exit and oriented to impart to particles emerging from said exit a charge of a predetermined sign with a charge-tomass ratio of from about 1/ 10 elementary charges per nucleon to about 1/ 10 elementary charges per nucleon; and electrostatic particle acceleration means positioned to accelerate particles subjected to said charging means and adapted to be connected to a voltage source of a sign opposite said predetermined sign.

10. The apparatus claimed in claim 9 wherein said mechanical acceleration means is adapted to accelerate said particles at least about times the acceleration of gravity.

11. Particle acceleration apparatus, comprising: particle source means adapted to store therewithin particles to be accelerated; particle conveyor means disposed closely adjacent to said particle source means for conveying particles therefrom; mechanical particle acceleration means connected to said conveyor means for receipt of particles therefrom and adapted to mechanically impart to particles within said accelerator means an amount of kinetic energy; particle charging means disposed adjacent to said acceleration means and adapted to receive particles therefrom and to impart to them an electric charge of a predetermined sign, said charging means including an electron gun and an electron collector electrode positioned to define a particle charging region; and electrostatic particle acceleration means positioned adjacent to said charging means and adapted to subject particles subjected to said charging means to an electrostatic acceleration field thereby to impart to particles passing within said field an amount of kinetic energy, substantially larger than said initial amount of kinetic energy.

12. Particle acceleration apparatus, comprising: particle source means including a container having substantially rigid walls defining a chamber and having a flexible member disposed within said chamber and adapted to move inwardly of said walls toward a central region therewithin; particle conveyor means disposed at least partially within said central region and a worm gear positioned for conveying particles therefrom and connected to be rotated in a direction moving particles in a predetermined direction from said central region; mechanical particle acceleration means connected to said conveyor means for receipt of particles from said worm gear and adapted to mechanically impart to particles within said accelerator means an initial amount of kinetic energy; particle charging means disposed adjacent to said acceleration means and adapted to receive particles therefrom and to impart to them an electric charge of a predetermined sign, said charging means including an electron gun and an electron collector electrode positioned to define a particle charging region; and electrostatic particle acceleration means positioned adjacent to said charging means and adapted to subject particles subjected to said charging means to an electrostatic acceleration field thereby to impart to particles passing within said field an amount of kinetic energy substantially larger than said initial amount of kinetic energy.

} l3. Particle acceleration apparatus, comprising: particle source means including a container having rigid walls defining a chamber and having a flexible member disposed within said chamber and adapted to move inwardly of said walls toward a central region of said chamber; particle conveyor means disposed at least partially within said particle source means, and including a sleeve disposed at least partially within said central region and a worm gear positioned within said sleeve, said sleeve'having at least one aperture communicating with the region within which said worm gear is disposed and with a portion of said central region outside of said sleeve; mechanical particle separator means connected to said conveyor means for receipt of particles from said worm gear, said separator means having a particle exit orifice and including vibrator means connected to said separator means for imparting to particles within said separator means an initial acceleration thereby to provide a distribution of particles therewithin; and particle charging means including an electron gun and an electron collector electrode positioned to define a particle charging region adjacent to said orifice and adapted to impart to particles emerging from said orifice an electric charge of a predetermined sign; an electrostatic particle acceleration means positioned adjacent to said charging means and adapted to subject particles charged by said charging means to an electrostatic acceleration field of a sign opposite said predetermined sign thereby to impart to articles passing within said electrostatic field an additional amount of kinetic energy.

14. Particle acceleration apparatus, comprising: particle source means including a container having rigid walls defining a chamber and having a flexible member disposed within said chamber and adapted to move toward a central region of said chamber; particle conveyor means disposed at least partially within said particle source means, and including a sleeve disposed at least partially within said central region and a worm gear positioned within said sleeve, said sleeve having at least one aperture communicating with the region within which said worm gear is disposed and with a portion of said central region outside of said sleeve; mechanical particle acceleration means connected to said conveyor means for receipt of particles from said worm gear, said mechanical acceleration means having a particle exit orifice and including vibrator means connected to said accelerator means for imparting an initial acceleration to particles within said accelerator means thereby to provide a distribution of particles within said particle acceleration means; particle charging means including an electron gun and an electron collector electrode positioned to define a particle charging region adjacent to said orifice and adapted to impart to particles emerging from said orifice a charge of a predetermined sign; and a space charge limited electrostatic particle acceleration gun positioned adjacent to said charging means and adapted to subject particles charged by said charging means to an electrostatic acceleration field of a sign opposite said predetermined sign thereby to impart kinetic energy toparticles passing within said electrostatic field; and neutralizing means electrically connected to said mechanical acceleration means and constructed to emit charged particles of a sign opposite said predetermined sign.

15. Particle acceleration method comprising the steps of: first mechanically separating from each other each of a number of particles having a radius at least as small as about one micron; then imparting an electric charge to said particles; and finally subjecting the charged particles to an electrostatic acceleration field for accelerating them to a velocity of between about 5 kilometers per second and about 50 kilometers per second.

16. Particle acceleration method comprising the steps of: electrically charging particles to impart to them a mass to charge ratio of from about 10 to about 10 nucleons per elementary charge; and then subjecting the charged particles to an electrostatic acceleration field with an applied potential of from about 10 kilovolts to about kilovolts.

l7. Particle acceleration method comprising the steps of: electrically charging particles to import to them a mass to charge ratio of from about 10 to about 10 nucleons per elementary charge; and then subjecting the charged particles to a space charge limited electrostatic acceleration gun with an applied potential of from about 10 kilovolts to about 100 kilovolts.

18. Particle acceleration method comprising the steps of: electrically charging particles to impart to them a mass to charge ratio of from about 10 to about 10 nucleons per elementary charge; then subjecting the particle mass and charge and adjusting said applied potential to impart to said particles a velocity of from about 5 kilometers per second to about 50 kilometers per second.

19. Particle acceleration method comprising the steps of: electrically charging particles of a predetermined mass to impart to them a mass to charge ratio of from about 10 to about 10 nucleons per elementary charge; then subjecting the charged particles to a space charge limited electrostatic acceleration gun with an applied potential of from about 10 kilovolts to about 100 kilovolts for emission thereof; selecting the particle mass and charge and adjusting said applied potential to impart to said particles a velocity of from about 5 kilometers per second to about 50 kilometers per second; and emitting other particles having a mass appreciably less than that of said first named particles and a charge of a sign opposite that of said first named particles to neutralize the efiect of the first-named emission.

References Cited in the file of this patent UNITED STATES PATENTS 2,778,945 Burk Jan. 22, 1957 2,798,181 Foster July 2, 1957 2,808,510 Norton Oct. 1, 1957 2,818,507 Britten Dec. 31, 1957 2,819,423 Clark Jan. 7, 1958 2,826,708 Foster Mar. 11, 1958 

